1. Field of the Invention
The present invention relates to an optical characteristic measuring apparatus suitable for taking measurements of a surface light source and the like.
2. Description of the Background Art
Recently, development of new light sources such as LED (Light Emitting Diode) and EL (Electro Luminescence) has been advancing rapidly. As an indicator for evaluating the performance of such light sources, the total luminous flux (lm: lumen) is often used.
In order to measure the total luminous flux of such a light source, an integrating sphere (spherical photometer) is commonly used that is a hollow sphere in which a diffuse reflective material such as barium sulfate or PTFE (polytetrafluoroethylene) is applied to the inner wall surface of the hollow sphere. In the case of a measurement method using the integrating sphere, a light source arranged at the center of the integrating sphere is lit, the light radiated from the light source is repeatedly reflected from the inner wall surface, and accordingly the illuminance on the inner wall surface is made uniform. The fact that the illuminance on the inner wall surface which has thus been made uniform is proportional to the total luminous flux of the light source is utilized to calculate the total luminous flux of the light source.
In the case of the measurement method using the integrating sphere, however, the light source is arranged at the center inside the integrating sphere, and therefore, a measurement error may arise due to absorption of light by a structure arranged for supporting the light source, absorption of light by a baffle arranged for preventing the light from the light source from directly irradiating an optical receiver, and absorption of light by the light source itself, and the like.
For example, according to JIS C 8152:2007 “Measuring Methods of White Light Emitting Diode (LED) for General Lighting,” use of a method for determining a self-absorption correction factor of the light source is recommended. This method, however, cannot make corrections for absorption of light by the structure arranged for supporting the light source and absorption of light by the baffle.
Japanese Patent Laying-Open No. 06-167388 and Japanese Patent Laying-Open No. 2009-103654 each disclose a hemispherical photometer. This hemispherical photometer does not require the structure arranged for supporting the light source and therefore can avoid the influence of absorption of light by this structure. Moreover, the hemispherical photometer can correct errors due to self absorption of light by the light source by means of a simple configuration as disclosed in Japanese Patent Laying-Open No. 2009-103654.